A prior art device described in Japanese Patent Application Publication No. 2001-338506 includes an electric ballast for a vehicle lighting system that comprises a lamp housing with front and rear openings, a front lens closing the front opening, a discharge lamp put in the housing, and a reflector put in the housing to reflect light of the lamp toward the lens. The ballast is formed of a ballast housing closing said rear opening, and an inverter and an igniter which are put in the ballast housing. The ballast is also electrically connected with the lamp via a wire harness (wires and connectors) and a lamp socket.
Another prior art device described in Japanese Patent Application Publication No. 2002-367414 includes an electric ballast for a vehicle lighting system that comprises a lamp housing with front and rear openings, a front lens closing the front opening, a cap closing the rear opening, a discharge lamp put in the housing, and a reflector put in the housing to reflect light of the lamp toward the lens. This ballast is formed of an inverter mounted on the inner face of the cap, and an igniter put in a lamp socket within the lamp housing. These inverter and igniter are electrically connected each other through a wire harness including wires.
In these prior art devices and other similar prior art devices (e.g., France Patent Publication No. 2776365, U.S. Pat. No. 6,364,515 and Japanese Patent Application Publication Nos. 2001-101908 and 2002-343128), the wires within a lamp housing need be covered with a costly sheath shield such as a mesh shield or the like in the same way as, for example, a device described in Japanese Patent Application Publication No. 2000-195685. Because there is a possibility that noise generated from a discharge lamp caused by polarity inversing of a lamp current enters each portion of a ballast through the wires to cause wrong operation of devices.
Other prior art devices described in Japanese Patent Application Publication Nos. 2001-101909 and 2003-317535 are provided with a ballast housing that includes a lamp socket or a discharge lamp in addition to an inverter and an igniter. According to these devices, the need of said sheath shield is eliminated. However, if the ballast housing does not have a shield function, said possibility of the wrong operation remains. In the latter, especially, a seal member (insulating member or elastic moulding) exposed from the inside of the ballast housing touches the lamp housing. The former also has the ballast housing inside the lamp housing, and accordingly its ballast is exposed to high temperature within the lamp housing, so that heat generating parts (high temperature parts) of the ballast become extremely high temperature.
It is an object of the present invention to eliminate the need of a shield sheath in a lamp housing, and also to protect heat generating parts of an electric ballast from high temperature in the lamp housing.